Current wavelength division multiplexed (WDM) lightwave communication systems strive for maximum transmission capacity by spacing optical channels as closely as possible, typically about or less than a nanometer (nm). Additionally, in such lightwave communication systems, Erbium (Er) doped optical fiber amplifiers are typically used to maintain the amplitude and integrity of the optical signals over long distance spans. While transmission capacity is greatly increased, it cannot be overlooked that stable lasing transmission wavelengths are critical to system operation inasmuch as any drift of the laser's wavelength readily causes signals from one optical channel to cross into another. As such, current designs for WDM communication systems specify relatively stable, narrow linewidth transmission lasers, typically employing external fiber gratings to stabilize the lasing wavelengths with variations in temperature.
In such communication systems, a factor affecting the optical gain of the Er-doped fiber amplifier (EDFA) is the wavelength used to optically pump the optical signals. Due to its higher gain efficiency, it is preferable to pump near the 980 nm absorption band of the Erbium. For reliability considerations, however, several low power pump lasers may be employed to generate the required pump power levels.
In current WDM lightwave communication systems, pump lasers are also required to lase precisely at predetermined wavelengths. One drawback to this design approach is the precise wavelength stabilization requirements for the pump lasers.